OK this one has me stumped. Car has run great for a while now, then suddenly one morning its starts backfiring as I accelerate and decelerate. Not a loud timing backfire but more of a popping sound. I thought it might be my air:fuel mixture so I tuned it and no improvement. Checked the timing and all looks good. Read on a few threads that popping could be due to an exhaust leak igniting unburnt fuel. Seemed like a possibility as my headers drop down below my frame and are flat and scuffed us from hitting speed bumps. One may have finally given way. But I don't hear a ticking sound like a header gasket leak so I'm not sure. I also read about backfires from fuel ignited in the engine and was doing a visual check today and noticed that manifold gasket is bulging out about a 1/4" between the number 3 and 5 cylinders. Looks like its covered in oil. I also have been noticing the car running through oil quickly. Could a manifold gasket leak be causing fuel to ignite and cause a backfire? Could oil be getting into the 3 and 5 cylinders? My son drive the car and said he occasionally saw smoke from the rear of the car. Just need a place to start...any thoughts?